Multiple-Input Multiple-Output (MIMO) is a scheme that can increase transmission/reception data efficiency by employing a plurality of transmission antennas and a plurality of reception antennas, beyond the traditional use of a single transmission antenna and a single reception antenna. That is, a transmitting end or a receiving end increases capacity or improves performance by use of multiple antennas. Thus, MIMO is also called a multi-antenna technology. For reliable multi-antenna transmission, the transmitting end needs to receive a channel information feedback from the receiving end.
While a single carrier is configured for each of uplink and downlink in a legacy wireless communication system, the introduction of Carrier Aggregation (CA) or a multi-carrier technology that aggregates a plurality of carriers is under discussion in order to support an extended bandwidth.